1. Field of the Invention
The present invention relates generally to asynchronous Wideband Code Division Multiple Access (WCDMA) communications. In particular, the present invention relates to a method of setting a gain factor representing a power variable for uplink packet transmission.
2. Description of the Related Art
As a 3rd generation mobile communication system using WCDMA based on the European Global System for Mobile communications (GSM) system, Universal Mobile Telecommunication Service (UMTS) provides mobile subscribers or computer users with a uniform service of transmitting packet-based text, digitized voice, and video and multimedia data at or above 2 Mbps, irrespective of their locations around the world. With the introduction of the concept of virtual access, the UMTS system allows access to any end point within a network all the time. This virtual access refers to packet-switched access using a packet protocol like Internet Protocol (IP).
FIG. 1 illustrates the configuration of an exemplary UMTS Terrestrial Radio Access Network (UTRAN) in a typical UMTS system.
Referring to FIG. 1, a UTRAN 12 comprises Radio Network Controllers (RNCs) 16a and 16b and Node Bs 18a to 18d, and connects a User Equipment (UE) 20 to a Core Network (CN) 10. A plurality of cells may underlie the Node Bs 18a to 18d. Each RNC 16a or 16b controls its underlying Node Bs, and each Node B controls its underlying cells. An RNC, and Node Bs and cells under the control of the RNC, collectively form a Radio Network Subsystem (RNS) 14a or 14b. 
The RNCs 16a and 16b each allocate or manage radio resources to the Node Bs 18a to 18d under their control, and the Node Bs 18a to 18d function to actually provide the radio resources. The radio resources are configured on a cell basis, and the radio resources provided by the Node Bs 18a to 18d refer to radio resources of the cells that they manage. The UE 20 establishes a radio channel using radio resources provided by a particular cell under a particular Node B, for communications. From the UE's point of view, a distinction between the Node Bs 18a to 18d and their controlled cells is of little importance, and the UE 20 deals only with a physical layer configured on a cell basis. Therefore, the terms “Node B” and “cell” are interchangeably used herein.
A Uu interface is defined between a UE and an RNC. The hierarchical protocol architecture of an exemplary Uu interface is illustrated in detail in FIG. 2. This interface is divided into a control plane (C-plane) 30 for exchanging control signals between the UE and the RNC, and a user plane (U-plane) 32 for transmitting actual data.
Referring to FIG. 2, a C-plane signal is processed in a Radio Resource Control (RRC) layer 34, a Radio Link Control (RLC) layer 40, a Medium Access Control (MAC) layer 42, and a physical (PHY) layer 44. A U-plane signal is processed in a Packet Data Control Protocol (PDCP) layer 36, a Broadcast/Multicast Control (BMC) layer 38, the RLC layer 40, the MAC layer 42, and the PHY layer 44. The PHY layer 44 resides in each cell, and the MAC layer 42 through the RRC layer 34 are usually configured in each RNC.
The PHY layer 44 provides an information delivery service by a radio transfer technology, corresponding to Layer 1 (L1) in an Open System Interconnection (OSI) model. The PHY layer 44 is connected to the MAC layer 42 via transport channels. The mapping relationship between the transport channels and physical channels is determined according to how data is processed in the PHY layer 44.
The MAC layer 42 is connected to the RLC layer 40 via logical channels. The MAC layer 42 delivers data received from the RLC layer 40 on the logical channels to the PHY layer 44 on appropriate transport channels, and delivers data received from the PHY layer 44 on the transport channels to the RLC layer 40 on appropriate logical channels. The MAC layer 42 inserts additional information or interprets inserted data in data received on the logical channels, and controls random access. A U-plane part is called MAC-data (MAC-d) and a C-plane part is called MAC-control (MAC-c) in the MAC layer 42.
The RLC layer 40 controls the establishment and release of the logical channels. The RLC layer 40 operates in one of an Acknowledged Mode (AM), an Unacknowledged Mode (UM), and a Transparent Mode (TM), and provides different functionalities in each mode. Typically, the RLC layer 40 segments or concatenates Service Data Units (SDUs) received from an upper layer to an appropriate size, and corrects errors.
The PDCP layer 36 resides above the RLC layer 40 in the U-plane 32. The PDCP layer 36 is responsible for compression and decompression of the header of data carried in the form of an IP packet and data delivery with integrity in the case where a serving RNC is changed due to the UE's mobility.
The characteristics of the transport channels that connect the PHY layer 44 to the upper layers depend on a Transport Format (TF) that defines PHY layer processes, including convolutional channel encoding, interleaving, and service-specific rate matching.
Particularly, the UMTS system uses the Enhanced Uplink Dedicated CHannel (E-DCH) with the aim to further improve packet transmission performance on the uplink from UEs to a Node B. The E-DCH is enhanced from the legacy DCH. To support more stable high-speed data transmission, the E-DCH utilizes Hybrid Automatic Retransmission request (HARQ) and Node B-controlled scheduling.
FIG. 3 illustrates a typical data transmission on the E-DCH via radio links. Reference numeral 100 denotes a Node B supporting the E-DCH and reference numerals 101 to 104 denote UEs that transmit the E-DCH.
Referring to FIG. 3, the Node B 100 evaluates the channel status of the UEs 101 to 104, and schedules their uplink data transmissions based on the channel status of each. The scheduling is performed such that a noise rise measurement does not exceed a target noise rise in the Node B 100 in order to increase total system performance. Therefore, the Node B 100 allocates a low data rate to a remote UE 104 and a high data rate to a nearby UE 101.
FIG. 4 is a diagram illustrating a typical signal flow for message transmission on the E-DCH.
Referring to FIG. 4, a Node B 200 and a UE 201 establish an E-DCH in step 202. Step 202 involves message transmission on dedicated transport channels. The UE 201 transmits its UE status information to the Node B 200 in step 204. The UE 201 status information may contain uplink channel status information represented by the transmit power and power margin of the UE 201, and the amount of buffered data to be transmitted to the Node B 200.
In step 206, the Node B 200 monitors UE status information from a plurality of UEs to schedule uplink data transmissions for the individual UEs. The Node B 200 can decide to approve an uplink packet transmission from the UE 201 and then transmit scheduling assignment information to the UE 201 in step 208. The scheduling assignment information includes an allowed data rate and an allowed timing.
In step 210, the UE 201 determines the TF of the E-DCH based on the scheduling assignment information. The UE 201 then transmits to the Node B 200 TF information, that is, a Transport Format Resource Indicator (TFRI) and uplink packet data, on the E-DCH at the same time in steps 212 and 214. The Node B 200 then determines whether the TFRI and the uplink packet data have errors in step 216. In the absence of errors in both, the Node B 200 transmits an ACKnowledgement (ACK) signal to the UE 201, whereas in the presence of errors in either of the TFRI and the uplink packet data, the Node B 200 transmits a Non-ACKnowledgement (NACK) signal to the UE 201 in step 218.
In the former case, the packet data transmission is completed and the UE 201 transmits new packet data to the Node B 200 on the E-DCH. However, in the latter case, the UE 201 retransmits the same packet data to the Node B 200 on the E-DCH.
Compared to the legacy DCH, the E-DCH operated as described above supports Adaptive Modulation and Coding (AMC), HARQ, Node B-controlled scheduling, and shorter Transmission Time Interval (TTI), in order to support more stable, high-speed data transmission.
Uplink dedicated physical channels include a Dedicated Physical Data CHannel (DPDCH) to which the legacy DCH is mapped, a Dedicated Physical Control CHannel (DPCCH) for delivering control information associated with the DPDCH, a High Speed DPCCH (HS-DPCCH) for delivering uplink control information associated with High Speed Downlink Packet Access (HSDPA), an Enhanced DPDCH (E-DPDCH) to which the E-DCH is mapped, and an Enhanced DPCCH (E-DPCCH) for delivering control information associated with the E-DPDCH.
Traditionally, the transmit power of the E-DPDCH is decided relative to that of the DPCCH. The DPCCH is a criterion by which the transmit power of all other uplink dedicated physical channels is decided. The E-DCH can be sent along with the legacy DCH, or independently without the legacy DCH. The latter is called a stand-alone E-DCH. When the stand-alone E-DCH is used, the DPDCH to which the DCH is mapped, does not exist in the PHY layer.
Accordingly, a need exists for a system and method for determining the transmit power of the stand-alone E-DCH.